I checked my RV-12 voltage with two meters, the engine off, master switch on and avionics on. One meter read 12.35 and the other read 12. 25. The meter average is 12.3. The Dynon D-180 voltage was 12.1 for a difference of 0.2 volts. While flying, my D-180 displays 13.6 volts. If the Dynon EMS voltmeter is anything like handheld digital voltmeters, there could very well be slight variations between Dynon units.
Batteries should be charged with a little over 14 volts. Once charged, a battery should be maintained at 13.2 volts. My Rotax starts so quickly that the battery is seldom discharged. So it does not require recharging, only maintaining. I bought a Schumacher 1562 battery charger-maintainer, for about $20 at Wal-Mart, for maintaining the battery voltage on the ground during periods of disuse. Bob Nuckolls at AeroElectric recommended it. I recommend his website for gaining knowledge about aircraft electrical systems.
http://forums.matronics.com/viewforum.php?f=3
I think that the Rotax voltage regulator installed in the RV-12 puts out adequate voltage at 13.6 or above as displayed on the Dynon. More voltage is not necessarily better and could do more harm than good.
For those who wish to boost the regulator output voltage, I have an idea but have never actually tried it: Connect a diode in series with the small yellow wire that goes to the regulator "C" terminal (Voltage Sense). The diode arrow (banded end) should point towards the regulator. The voltage-sense wire in the original avionics package is not protected by a fuse.
Sometimes voltage regulators put out too high of a voltage. This can be caused by a loose or corroded connection someplace in the voltage-sense wire or between the regulator case and ground.
Joe Gores